Fluoroelastomers are elastomers prepared by curing a fluoroelastomer precursor (“gum”) made from monomers containing one or more atoms of fluorine, or copolymers of such monomers with other monomers, the fluoromonomer(s) being present in the greatest amount by mass. The fluoroelastomer precursor is a fluoropolymer that is suitable to prepare a fluoroelastomer having desired elasticity properties. Typically, the fluoroelastomer precursor is an amorphous fluoropolymer or a fluoropolymer that hardly shows a melting point. Fluoroelastomers have been used successfully in a number of applications due to their ability to withstand high temperatures and aggressive chemicals, as well as the ability of the fluoroelastomer gum to be processed using standard elastomer processing equipment. In addition, fluoroelastomers have been used in fuel management systems such as automotive fuel hoses, filler neck hoses, injector o-rings, and the like. Fuel management applications require low fuel vapor permeation in combination with good low temperature properties, sealability, and flexural properties.
Fluoroelastomers with high fluorine content show good fuel permeation resistance. However, high-fluorine content fluoroelastomers such as high-fluorine content terpolymers based on tetrafluoroethylene, vinylidene fluoride, and hexafluoropropylene have some limitations. For example, when the tetrafluoroethylene content (and thus the fluorine content) is high, flexibility and processability tend to be compromised. With respect to processability, the high fluorine content may render a fluoroelastomer too stiff for curative incorporation on standard processing equipment such as roll mills or Banbury mixers, which requires a material with a melting point less than about 100° C. On the other hand, when the hexafluoropropylene content, at the expense of vinylidene fluoride, is too high, the polymerization rate may become unacceptably slow for commercial production.
To overcome some of the limitations associated with the use of TFE/HFP/VDF copolymers (also known as THV copolymers), U.S. Pat. No. 6,310,141 teaches blending the THV fluoroelastomer precursor with a fluoroplastic.
U.S. Pat. No. 4,696,989 also discloses THV copolymers for producing fluoroelaslomers. In particular, this patent teaches specific ratios of the composing monomers in the ternary diagram as yielding fluoroeiastomers that are particularly suitable for use in wire coating where good insulating performance, moldability, heat resistance, flame retardance and flexibility are desired. U.S. Pat. No. 4,696,989 is not specifically concerned with providing fluoroelastomers that have excellent properties for use in fuel management systems.
Despite the many known nuoroelastomers, and in particular THV fluoroelastomers, there continues to be a desire to find further THV based fluoroelastomer compositions that have excellent properties for use in fuel management systems. In particular, it is a desire to find THV based fluoroelastomers that can be manufactured in a convenient and cost effective way, that have good processing properties, good flexibility and that have properties that make them particularly suitable for use in a fuel management system. Thus, it will typically be desired that the THV fluoroelastomers have low gas and fuel vapor permeation.